It would be either Minna no Combini or Minna no Comvini. (I've never seen anyone write it the second way.)
At any rate, the title means "Everyone's Convenience Store".
Well, the short answer to "Why aren't they writing things the way I want!!" is that scene release groups usually subscribe to the GameFAQs method of romanization (ie; they go to GameFAQs and see how they romanized it).
The long answer is this (a bunch of google searches):
There you go, the standardized way of romanizing that word only gets about 200k results while the way that made you all upset enough to call some dude who probably doesn't even know Japanese pathetic got nearly 2 million.
That's the power of GameFAQs folks, if you don't like it, you can spend all day editing info on their site.
wait... the real reading is Combini right? well the publisher is same as Mama series, we'll see the title would be Mama Convience Store... man that sucks anyway, since I'm bored with DS, this game will be my new game... I think...